1. Field of the Invention
The present invention relates to a water-decomposable absorbent article for sanitary napkins, panty liners, disposable diapers, pads for urinary incontinence and the like.
2. Description of the Related Art
Conventionally, the absorbent articles such as the sanitary napkins, the panty liners, the disposable diapers, and the pads for urinary incontinence are widely used for serving as absorbing body wastes. The absorbent articles are discarded as wastes, after having been used. However, the wastes of such absorbent articles are increasing in these days, and their volume is now an object of public concern. In addition, it is troublesome to treat the used absorbent articles as the wastes. Accordingly, absorbent articles composed of water-decomposable components and capable of being disposed of in toilets after use are now under study.
Japanese Unexamined Patent Publication (Kokai) No. Heisei 9-228241 discloses a water-decomposable non-woven fabric usable for a top sheet of absorbent articles. This non-woven fabric can be obtained through water-jetting treatment of a fibrous web that comprises regenerated cellulose having a fiber length of from 4 to 20 mm and pulp. Japanese Unexamined Patent Publication (Kokai) No. Heisei No. 5-25764 discloses a water-decomposable non-woven fabric usable for a surface member of absorbent articles. This non-woven fabric can be obtained by bonding fibers together with an unsaturated carboxylate copolymer serving as a binder. Japanese Unexamined Patent Publication (Kokai) No. Heisei 8-38547 discloses a water-decomposable absorbent sanitary article. This sanitary article comprises a surface layer formed by adding polyvinyl alcohol as a binder to water-dispersible fibers, a water-dispersible absorbent layer, and a water-soluble film. Japanese Unexamined Patent Publication (Kokai) No. Heisei 6-101154 discloses a water-degradable non-woven fabric containing a cellulose derivative as a binder therein. It also discloses an absorbent article comprising a top sheet of the water-degradable non-woven fabric, an absorbent layer of a pulp fiber sheet, and a back sheet of a polyvinyl alcohol film. Japanese Unexamined Patent Publication (Kokai) No. Heisei No. 8-19571 discloses a water-decomposable absorbent sanitary article. This absorbent sanitary article comprises a top layer of a water-dispersible non-woven fabric, an absorbent layer comprising water-dispersible absorbent paper, and a back layer formed by laminating polymethyl methacrylate on a film made of polyvinyl alcohol. Japanese Unexamined Patent Publication (Kokai) No. Heisei 10-85258 discloses a water-decomposable top sheet for absorbent articles, which is formed of a non-woven fabric comprising pulp and synthetic fibers. The top sheet can be readily peeled off from the other part (the side parts formed of synthetic fibers) of the absorbent article to which it is bonded, and can be disposed of in flush toilets.
Water-decomposable absorbent articles and water-decomposable top sheets must have good decomposability in water and high strength, while the two properties are contradictory to each other. With the prior art products set forth above, the decomposability in water and the strength are both limited. Specifically, enhancing the decomposability in water of the sheets will inevitably lead to the reduction of the strength thereof. Accordingly, the requirements for attaining well-balanced, good decomposability in water and high strength of absorbent articles are severe, and it is difficult to continuously produce the absorbent articles having well-balanced decomposability in water and strength.
An object of the present invention is to provide an absorbent article of which a surface member has good decomposability in water and high strength.
According to one aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back sheet, a water-decomposable absorbent layer, and a surface member covering the absorbent layer,
wherein the surface member includes a plurality of water-retentive water-decomposable sheets laminated and bonded to each other by integration means for permitting to dissociate the water-decomposable sheets from each other when wetted.
In the absorbent articles of the invention, the water-decomposable surface member has realized two contradictory functions of high decomposability in water after use and high durability during use. Specifically, in the invention, at least two water-decomposable sheets, which, however, are not satisfactorily durable enough for practical use when used individually, are integrally laminated to form the surface member of the absorbent articles, so that the laminated surface member exhibits high strength while having good decomposability in water.
Preferably, the integration means comprises mechanical means for bonding the water-decomposable sheets to each other. In this case, the mechanical means is needling for processing the water-decomposable sheets to have through-holes under the condition where the water-decomposable sheets are laminated, so that fibers constituting each the water-decomposable sheet are entangled around the through-holes. On the other hand, the mechanical means may be embossing the water-decomposable sheets under the condition where the water-decomposable sheets are laminated.
Preferably, the integration means is bonding the water-decomposable sheets to each other with a water-soluble adhesive.
Also preferably, the integration means is bonding the water-decomposable sheets to each other through hydrogen bonding, while in dry.
It is preferable that, the ratio of the water retention of one water-decomposable sheet to that of another adjacent to the sheet falls between 40:60 and 60:40, when the surface member are wetted.
Preferably, the water-decomposable sheets constituting the surface member each contain from 30 to 100% by weight of hydrophilic fibers.
Also preferably, each water-decomposable sheet has a weight (Metsuke) falling between 10 and 60 g/m2.
Also preferably, each water-decomposable sheet has a degree of decomposition in water of at most 100 seconds, measured according to JIS P-4501 using Magnetic Stirrer MM-ST manufactured by MITAMURA RIKEN CO., LTD. Also preferably, the surface member comprising a plurality of such water-decomposable sheets has a degree of decomposition in water of at most 100 seconds, measured according to JIS P-4501.
Also preferably, the surface member comprising at least two water-decomposable sheets bonded to each other by the integration has a tensile strength in dry of at least 1000 g/25 mm, measured according to JIS P-8113 using Tensile Tester AUTOGRAPH (AGK-IKNG) manufactured by SHIMADZU CORPORATION.
Also preferably, the surface member comprising at least two water-decomposable sheets has a tensile strength in wet of at least 200 g/25 mm measured according to JIS P-8135.